1. Field of Invention
This invention relates to optical systems and more particularly to methods media and signals for determining optimum pre-compensation and performance of an optical system.
2. Description of Related Art
Dispersion managed RZ systems have been widely studied for use in large capacity digital transmission systems. Such systems typically involve an optical system comprised of a plurality of optical links. Each optical link may present some degree of dispersion to signals transmitted on the medium. Normally such dispersion is reduced by use of a dispersion compensation module (DCM). However, such modules do not perfectly reduce dispersion and each one may compensate its respective optical medium to a different degree. There are statistical variations in dispersion and dispersion slope in DCMs and length variations in optical media which make it difficult to optimize the pre-compensation required for improving system performance.
As a result of the above variations, optimization of pre-compensation has become increasingly important for improving system performance, especially in the real field deployment of the system, where transmission link design restrictions and fiber properties are far from ideal. Dispersion by each span of an optical system is often represented by a dispersion map. It has been known that optimum pre-compensations vary significantly with dispersion maps. Without optimization of the pre-compensation, system performance can be severely penalized. Simple and effective procedures for calculating the optimum pre-compensations for different dispersion maps do not exist Current methods for calculation involve running simulations on every individual dispersion map.
Work by F. Favre et al. entitled "Experimental evidence of pseudo-periodical solution propagation in dispersion-managed link", in Electronics Letters, Vol. 34, No. 19, p1868, (1998); and F. Neddam et al. entitled "Analytical optimization of dispersion-managed solution propagation in long-haul WDM systems and experimental verification", in Electronics Letters, Vol 35, No. 13, p1093, (1999) have addressed the problem of pre-compensation. These works suggest an optimization method involving calculating the optimum solution pulse breathing conditions in single channel or WDM systems. Although qualitative agreements have been achieved between the theory and experiments, the method involves complicated calculations, which must be repeated whenever a dispersion map or wavelengths in a WDM system change.
Work by Ekaterina A. Golovchenko et al. entitled "Modeling vs Experiments of 16.times.10 Gb/s WDM Chirped RZ Pulse Transmission over 7500 km", in OFC/IOOC '99. Technical Digest, vol.3, p. 246, (1999) has also addressed the problem. This work suggests a simulation technique, through which the optimum pre-compensation can be obtained during the optimization of system performance. The simulation technique is intended for system performance optimization rather than a procedure for calculating optimum pre-compensation and again, the suggested process must be repeated in the event of a dispersion map or wavelength change.
A simple and effective method to calculate the optimum pre-compensations for different dispersion maps is very much desired.